Heterogeneity among AIDS retroviral genomes has been clearly demonstrated. We have used molecular cloning, restriction enzyme analysis, and nucleotide sequencing techniques to characterize isolates of the human immunodeficiency virus (HIV). These studies may provide data regarding their structural as well as geographic diversity and, possibly, the degree of antigenic variation and pathogenicity among different HIV isolates. An African isolate (Zaire-2) and a North American isolate (NY-5) of HIV-1 were molecularly cloned using lambda bacteriophage vectors. Each clone contained a single LTR (9.2 kb genome) and, upon transfection of lambda clones into lymphocytes, infectious virus particles were produced. Reverse transcriptase (RT) activity resembled that of the constructed infectious clone (pNL4-3) and, upon passage of supernatants onto fresh lymphocytes, displayed similar RT kinetics of pNL4-3. The complete nucleotide sequence of each of these infectious molecular clones has now been analyzed, and attempts to prepare antisera of each isolate for neutralization tests are in progress. A T cell clone (ACH-2) from T cells infected with HIV-1 produced HIV-1 in response to stimulation with phorbol myristic acetate (PMA). This isolate was molecularly cloned and, upon transfection into lymphocytes, produced virus; however, only in the presence of PMA. Passage onto fresh lymphocytes produced virus as monitored by RT in the absence of the inducing PMA. Presently, we are studying the biological role of PMA in viral induction of HIV-1 and the relationship of latency in viral infection.